When drilling a subsea wellhead, a wellhead housing will typically be located on the sea floor and a casing lowered into the well and cemented into place. A casing hanger is supported in the wellhead housing and is secured to the upper end of the casing. A drill bit and a drill string from a drilling vessel pass downward through the wellhead housing and casing hanger for further drilling operations.
Various types of wear bushings have been devised to land on the casing hanger and limit wear to the wellhead housing, the hanger, and the casing suspended from the hanger. Some prior art wear bushings are interconnected with the casing hanger, which is conventionally supported in place by the wellhead. Other wear bushings are connected to the casing hanger seal, which in turn is supported on the casing hanger. In some applications, the casing hanger may migrate upward in response to high fluid pressure below the hanger. Axial movement of the casing hanger and the wear bushing in response to fluid pressure in the well is detrimental to the overall purpose of the wear bushing, which is to reliably limit wear on the hanger and casing by the rotating drill pipe.
U.S. Pat. No. 5,199,495 discloses a split wear bushing which is supported on the casing hanger. U.S. Pat. No. 5,025,864 discloses a wear bushing that connects to the seal for the casing hanger. U.S. Pat. No. 5,360,063 discloses another type of wear bushing which is supported on the casing hanger. Other patents of interest include U.S. Pat. Nos. 4,362,210, 4,978,147, and 4,340,259.
The disadvantages of prior art overcome by the present invention, and improved wear bushing and running tool are hereinafter disclosed for connecting the wear bushing to the wellhead.